In geometry class, the girl to boy ratio is $2$ to $7$. If there are $10$ girls, how many boys are there?
Explanation: A ratio of $2$ girls to $7$ boys means that there is a group of $2$ girls for every group of $7$ boys. If there are $10$ girls, then there are $5$ groups of $2$ girls each. Because we know the ratio is $2:7$ , there must be $5$ groups of $7$ boys each. There is a total of $35$ boys in geometry class.